﻿// Copyright (c) Microsoft Corporation
// The Microsoft Corporation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System;
using System.Text.RegularExpressions;

namespace Microsoft.CmdPal.Ext.Calc.Helper;

public static class CalculateHelper
{
    private static readonly Regex RegValidExpressChar = new Regex(
        @"^(" +
        @"%|" +
        @"ceil\s*\(|floor\s*\(|exp\s*\(|max\s*\(|min\s*\(|abs\s*\(|log(?:2|10)?\s*\(|ln\s*\(|sqrt\s*\(|pow\s*\(|" +
        @"factorial\s*\(|sign\s*\(|round\s*\(|rand\s*\(\)|randi\s*\([^\)]|" +
        @"sin\s*\(|cos\s*\(|tan\s*\(|arcsin\s*\(|arccos\s*\(|arctan\s*\(|" +
        @"sinh\s*\(|cosh\s*\(|tanh\s*\(|arsinh\s*\(|arcosh\s*\(|artanh\s*\(|" +
        @"rad\s*\(|deg\s*\(|grad\s*\(|" + /* trigonometry unit conversion macros */
        @"pi|" +
        @"==|~=|&&|\|\||" +
        @"((-?(\d+(\.\d*)?)|-?(\.\d+))[Ee](-?\d+))|" + /* expression from CheckScientificNotation between parenthesis */
        @"e|[0-9]|0[xX][0-9a-fA-F]+|0[bB][01]+|0[oO][0-7]+|[\+\-\*\/\^\., ""]|[\(\)\|\!\[\]]" +
        @")+$",
        RegexOptions.Compiled);

    private const string DegToRad = "(pi / 180) * ";
    private const string DegToGrad = "(10 / 9) * ";
    private const string GradToRad = "(pi / 200) * ";
    private const string GradToDeg = "(9 / 10) * ";
    private const string RadToDeg = "(180 / pi) * ";
    private const string RadToGrad = "(200 / pi) * ";

    public static bool InputValid(string input)
    {
        if (string.IsNullOrWhiteSpace(input))
        {
            return false;
        }

        if (!RegValidExpressChar.IsMatch(input))
        {
            return false;
        }

        if (!BracketHelper.IsBracketComplete(input))
        {
            return false;
        }

        // If the input ends with a binary operator then it is not a valid input to mages and the Interpret function would throw an exception. Because we expect here that the user has not finished typing we block those inputs.
        var trimmedInput = input.TrimEnd();
        if (trimmedInput.EndsWith('+') || trimmedInput.EndsWith('-') || trimmedInput.EndsWith('*') || trimmedInput.EndsWith('|') || trimmedInput.EndsWith('\\') || trimmedInput.EndsWith('^') || trimmedInput.EndsWith('=') || trimmedInput.EndsWith('&') || trimmedInput.EndsWith('/') || trimmedInput.EndsWith('%'))
        {
            return false;
        }

        return true;
    }

    public static string FixHumanMultiplicationExpressions(string input)
    {
        var output = CheckScientificNotation(input);
        output = CheckNumberOrConstantThenParenthesisExpr(output);
        output = CheckNumberOrConstantThenFunc(output);
        output = CheckParenthesisExprThenFunc(output);
        output = CheckParenthesisExprThenParenthesisExpr(output);
        output = CheckNumberThenConstant(output);
        output = CheckConstantThenConstant(output);
        return output;
    }

    private static string CheckScientificNotation(string input)
    {
        /**
         * NOTE: By the time that the expression gets to us, it's already in English format.
         *
         * Regex explanation:
         * (-?(\d+({0}\d*)?)|-?({0}\d+)): Used to capture one of two types:
         * -?(\d+({0}\d*)?): Captures a decimal number starting with a number (e.g. "-1.23")
         * -?({0}\d+): Captures a decimal number without leading number (e.g. ".23")
         * e: Captures 'e' or 'E'
         * (-?\d+): Captures an integer number (e.g. "-1" or "23")
         */
        var p = @"(-?(\d+(\.\d*)?)|-?(\.\d+))e(-?\d+)";
        return Regex.Replace(input, p, "($1 * 10^($5))", RegexOptions.IgnoreCase);
    }

    /*
     * num (exp)
     * const (exp)
     */
    private static string CheckNumberOrConstantThenParenthesisExpr(string input)
    {
        var output = input;
        do
        {
            input = output;
            output = Regex.Replace(input, @"(\d+|pi|e)\s*(\()", m =>
            {
                if (m.Index > 0 && char.IsLetter(input[m.Index - 1]))
                {
                    return m.Value;
                }

                return $"{m.Groups[1].Value} * {m.Groups[2].Value}";
            });
        }
        while (output != input);

        return output;
    }

    /*
     * num func
     * const func
     */
    private static string CheckNumberOrConstantThenFunc(string input)
    {
        var output = input;
        do
        {
            input = output;
            output = Regex.Replace(input, @"(\d+|pi|e)\s*([a-zA-Z]+[0-9]*\s*\()", m =>
            {
                if (input[m.Index] == 'e' && input[m.Index + 1] == 'x' && input[m.Index + 2] == 'p')
                {
                    return m.Value;
                }

                if (m.Index > 0 && char.IsLetter(input[m.Index - 1]))
                {
                    return m.Value;
                }

                return $"{m.Groups[1].Value} * {m.Groups[2].Value}";
            });
        }
        while (output != input);

        return output;
    }

    /*
     * (exp) func
     * func func
     */
    private static string CheckParenthesisExprThenFunc(string input)
    {
        var p = @"(\))\s*([a-zA-Z]+[0-9]*\s*\()";
        var r = "$1 * $2";
        return Regex.Replace(input, p, r);
    }

    /*
     * (exp) (exp)
     * func (exp)
     */
    private static string CheckParenthesisExprThenParenthesisExpr(string input)
    {
        var p = @"(\))\s*(\()";
        var r = "$1 * $2";
        return Regex.Replace(input, p, r);
    }

    /*
     * num const
     */
    private static string CheckNumberThenConstant(string input)
    {
        var output = input;
        do
        {
            input = output;
            output = Regex.Replace(input, @"(\d+)\s*(pi|e)", m =>
            {
                if (m.Index > 0 && char.IsLetter(input[m.Index - 1]))
                {
                    return m.Value;
                }

                return $"{m.Groups[1].Value} * {m.Groups[2].Value}";
            });
        }
        while (output != input);

        return output;
    }

    /*
     * const const
     */
    private static string CheckConstantThenConstant(string input)
    {
        var output = input;
        do
        {
            input = output;
            output = Regex.Replace(input, @"(pi|e)\s*(pi|e)", m =>
            {
                if (m.Index > 0 && char.IsLetter(input[m.Index - 1]))
                {
                    return m.Value;
                }

                return $"{m.Groups[1].Value} * {m.Groups[2].Value}";
            });
        }
        while (output != input);

        return output;
    }

    // Gets the index of the closing bracket of a function
    private static int FindClosingBracketIndex(string input, int start)
    {
        var bracketCount = 0;    // Set count to zero
        for (var i = start; i < input.Length; i++)
        {
            if (input[i] == '(')
            {
                bracketCount++;
            }
            else if (input[i] == ')')
            {
                bracketCount--;
                if (bracketCount == 0)
                {
                    return i;
                }
            }
        }

        return -1;  // Unmatched brackets
    }

    private static string ModifyTrigFunction(string input, string function, string modification)
    {
        // Get the RegEx pattern to match, depending on whether the function is inverse or normal
        var pattern = function.StartsWith("arc", StringComparison.Ordinal) ? string.Empty : @"(?<!c)";
        pattern += $@"{function}\s*\(";

        var index = 0;    // Index for match to ensure that the same match is not found twice

        Regex regex = new Regex(pattern);
        Match match;

        while ((match = regex.Match(input, index)).Success)
        {
            index = match.Index + match.Groups[0].Length + modification.Length;    // Get the next index to look from for further matches

            var endIndex = FindClosingBracketIndex(input, match.Index + match.Groups[0].Length - 1);    // Find the index of the closing bracket of the function

            // If no valid bracket index was found, try the next match
            if (endIndex == -1)
            {
                continue;
            }

            var argument = input.Substring(match.Index + match.Groups[0].Length, endIndex - (match.Index + match.Groups[0].Length));  // Extract the argument between the brackets
            var replaced = function.StartsWith("arc", StringComparison.Ordinal) ? $"{modification}({match.Groups[0].Value}{argument}))" : $"{match.Groups[0].Value}{modification}({argument}))";  // The string to substitute in, handles differing formats of inverse functions

            input = input.Remove(match.Index, endIndex - match.Index + 1);    // Remove the match from the input
            input = input.Insert(match.Index, replaced);    // Substitute with the new string
        }

        return input;
    }

    public static string UpdateTrigFunctions(string input, CalculateEngine.TrigMode mode)
    {
        var modifiedInput = input;
        if (mode == CalculateEngine.TrigMode.Degrees)
        {
            modifiedInput = ModifyTrigFunction(modifiedInput, "sin", DegToRad);
            modifiedInput = ModifyTrigFunction(modifiedInput, "cos", DegToRad);
            modifiedInput = ModifyTrigFunction(modifiedInput, "tan", DegToRad);
            modifiedInput = ModifyTrigFunction(modifiedInput, "arcsin", RadToDeg);
            modifiedInput = ModifyTrigFunction(modifiedInput, "arccos", RadToDeg);
            modifiedInput = ModifyTrigFunction(modifiedInput, "arctan", RadToDeg);
        }
        else if (mode == CalculateEngine.TrigMode.Gradians)
        {
            modifiedInput = ModifyTrigFunction(modifiedInput, "sin", GradToRad);
            modifiedInput = ModifyTrigFunction(modifiedInput, "cos", GradToRad);
            modifiedInput = ModifyTrigFunction(modifiedInput, "tan", GradToRad);
            modifiedInput = ModifyTrigFunction(modifiedInput, "arcsin", RadToGrad);
            modifiedInput = ModifyTrigFunction(modifiedInput, "arccos", RadToGrad);
            modifiedInput = ModifyTrigFunction(modifiedInput, "arctan", RadToGrad);
        }

        return modifiedInput;
    }

    private static string ModifyMathFunction(string input, string function, string modification)
    {
        // Create the pattern to match the function, opening bracket, and any spaces in between
        var pattern = $@"{function}\s*\(";
        return Regex.Replace(input, pattern, modification + "(");
    }

    public static string ExpandTrigConversions(string input, CalculateEngine.TrigMode mode)
    {
        var modifiedInput = input;

        // Expand "rad", "deg" and "grad" to their respective conversions for the current trig unit
        if (mode == CalculateEngine.TrigMode.Radians)
        {
            modifiedInput = ModifyMathFunction(modifiedInput, "deg", DegToRad);
            modifiedInput = ModifyMathFunction(modifiedInput, "grad", GradToRad);
            modifiedInput = ModifyMathFunction(modifiedInput, "rad", string.Empty);
        }
        else if (mode == CalculateEngine.TrigMode.Degrees)
        {
            modifiedInput = ModifyMathFunction(modifiedInput, "deg", string.Empty);
            modifiedInput = ModifyMathFunction(modifiedInput, "grad", GradToDeg);
            modifiedInput = ModifyMathFunction(modifiedInput, "rad", RadToDeg);
        }
        else if (mode == CalculateEngine.TrigMode.Gradians)
        {
            modifiedInput = ModifyMathFunction(modifiedInput, "deg", DegToGrad);
            modifiedInput = ModifyMathFunction(modifiedInput, "grad", string.Empty);
            modifiedInput = ModifyMathFunction(modifiedInput, "rad", RadToGrad);
        }

        return modifiedInput;
    }
}
